Figure 45. A variant of Young’s double-slit experiment with light particles in which the photographic plate on the right is converted into a venetian blind and a pair of detectors are stationed behind it, each pointing at one of the slits. The experimenter operating the detectors can delay his decision right up to the moment each individual photon reaches the blind, whether to leave the blind closed and perform the usual double-slit experiment, producing interference fringes, or open it and verify which slit the photon came through. One might have thought this delayed choice would confuse the
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